ESTRO 2023 - Abstract Book

S369

Sunday 14 May 2023

ESTRO 2023

Quality assurance of radiotherapy target volume delineation (TVD) through peer review (PR) is an important requirement for delivery of safe and effective radiotherapy. However, PR takes time and in busy oncological practices in LMICs, such protected time is often not available. We present an audit of an on-demand PR process implemented in our centre. Materials and Methods 2 senior clinical oncologists (CO) providing site-specialised radiation gynaecological oncology agreed to an on-demand PR process whose outcomes were prospectively recorded. PR was performed before final contour approval to avoid delays.The initial TVD was completed by junior COs and then PR was done by senior COs. Treatment intent, staging, elective volumes, dose prescriptions and TVD were checked. Changes made were categorised as major change if TV was edited by more than 1 cm or to prevent geographical miss or where locoregional control could be affected. Other changes were categorised as minor changes. All patients planned for curative intent external beam radiotherapy from 15 Sept 2021 to 15 Sept 2022 were eligible for the study. A waiver of consent provided by the IRB and the protocol was prospectively registered (https://osf.io/wq4b5). The primary endpoints for the analysis were the proportion of patients where a major change was seen in GTV or CTV and the compliance with the peer review process. Results 231 patients with a median age of 55 years were evaluable. Majority (n = 176, 76%) had cervical cancer. 49 (21%) patients had para-aortic nodal involvement (pathological n = 15, radiological n = 34). Concurrent chemotherapy was planned for 182 (79%) patients. At least one PR session was conducted in 203 (88%) patients. More than one PR session was required in 3 patients (1.3%). Repeat PR sessions were mandated because of significant changes required in the treatment planning CT scan. Number of PR conducted per month ranged between 7 - 23. Major changes in TVD were required in 108 (53%) of the patients, while minor changes were necessitated in 69 (34%). Most of the patients (n = 77, 38%) required changes in the nodal CTV. Additional major modifications requested after the peer review included changes in the final stage in 7 (3.4%), change in treatment intent in 1 (0.5%), inclusion of para-aortic nodes in the elective nodal volume in 24 (11.8%), and a change in image registration in 5 (2.4%) of the patients. Major changes in organ at risk contours were required in 15 (7.3%) of the patients. The median working days required from the acquisition of planning CT to the contour approval time was 4 days (IQR 2 - 5 days). Anatomical locations of major modifications and proportion of modifications as per the type of cancer and treatment setting are illustrated in figures.

Conclusion An on-demand PR process was feasible and implementable while maintaining the treatment planning timelines. The high proportion of patients requiring major changes in TVD highlights the importance of PR as a quality assurance tool.

OC-0466 Verification of rectal cancer target auto-contouring by trained RTTs in online adaptive MRIgRT A. Betgen 1 , L. Wiersema 1 , N. Ferreira Silvério 1 , R. Simões 1 , C. Marijnen 1 , F. Peters 1 , U.A. van der Heide 1 , T. Janssen 1 1 The Netherlands Cancer Institute, Department of Radiation Oncology, Amsterdam, The Netherlands